1. Field of the Invention
The present invention relates to a solar cell module and more particularly relates to a solar cell module having front and rear surface members that are transmissive and which can let in light from both front and rear surfaces.
2. Description of the Prior Art
A solar cell can directly convert photo-energy from the sun that provides clean energy without depletion. Solar cell technology is expected to replace fossil fuel such as petroleum and coal. Since solar energy has been predicted to be the new energy source, a lot of effort has been made to commercialize solar cell technology. When using a solar cell as an energy source in practical general circumstances, a plurality of solar cells are connected electrically in serial or in parallel to increase output.
A description of a conventional solar cell module will be made by referring to FIGS. 13-16. FIG. 13 is a front view, FIG. 14 is a cross-sectional view at the A-A' line indicated in FIG. 13, and FIG. 15 is a rear elevation schematically illustrating a rear surface member which will be described later. FIG. 16 is an explanatory view illustrating an enlarged structure of an inside portion of a terminal box.
As shown in these figures, the solar cell module comprise of a front surface member 1 containing transmissive material such as glass and plastic, a rear surface member 2, and solar cells 3 . . . Generally a rear surface member 2 has a three-layered structure sandwiching an aluminum foil between resin films.
The solar cell 3 is, for example, one that contains crystalline Si substrate having p-n junction inside. Seventy-two units of solar cells 3 . . . are disposed in an 8.times.9 matrix shape and are connected electrically in serial with connection members 4 . . . containing a metal thin plate such as a copper thin plate. The solar cells 3 . . . are sealed between the front surface member 1 and the rear surface member 2 with sealing member 5, such as ethylene vinyl acetate (EVA), which is transmissive and insulated. A frame 6 formed by processible metal such as aluminum-is mounted around the sealing member.
Electricity generated in the solar cells 3 . . . is drawn to terminal boxes 50, 50 provided on a rear surface of the rear surface member 2 through electricity drawing wires 11, 11. Then, the electricity is output from the terminal boxes 50, 50 through an electric cable (not shown) to the outside.
In the above system which operates a plurality of solar cells connected in serial, the sunlight is sometimes prevented from being incident to a part of solar cells because of shade created from a building or snow drifts. In this case, a total voltage generated by the solar cells, which are normally operating, is applied to the above part of the solar cells as reverse voltage. If the reverse voltage reaches beyond a capacity voltage of the solar cells, the solar cells are broken. Otherwise, the above part of the solar cells generates heat, causing such problems as discoloration or foaming in the EVA sealing member or breakage of solar cells.
Thus, in order to overcome this problem, a common solar cell module has solar cells divided into several groups of a plurality of solar cells, and has means for preventing reverse voltage from being applied, which is connected to these solar cell groups in parallel.
For example, in the above solar cell module, 72 units of solar cells are divided into four groups of eighteen solar cells 3 . . . A diode 21, as means for preventing reverse voltage from being applied, is connected to these solar cell groups electrically in parallel and in reverse via connection wire 12. The diode 21, as shown in FIG. 16, is located in a terminal box 50, thus increasing the size of terminal box 50.
I the interim, a solar cell, which can generate energy from light which is incident not only from a front surface but from a rear surface, has been developed. A solar cell module, which employs such a solar cell that can take light from both front and rear surfaces, has a structure in which light can be incident to a rear surface of a solar cell through a rear surface member consisting of transmissive material such as glass rather than conventional material which is not transmissive.
However, in the solar cell module of the above structure, light which is incident from the rear surface is blocked by the terminal boxes 50, 50, the electricity drawing wires 11, 11, and the connection wires 12 . . . Because of the present configuration of the solar cell module light can not be incident to some parts of the rear surfaces of the solar cells. As a result, the solar cells of those parts generate electric current only by light which is incident from the front surface, and an electric current value of those parts becomes lower than others. Since a plurality of solar cells are connected electrically in serial, an output electric current value of the whole module becomes is lower for solar cells having the above configuration where light is not incident to the rear surface. Accordingly, light which is incident from the rear surface can not be utilized fully.
in addition to the above solar cell which can let in light from both front and rear surfaces, a solar cell module of sophisticated-design using a conventional solar cell, of which rear surface member is made of transmissive material and can transmit a part of light to the rear surface, has been provided. However, the terminal boxes 50, 50, electricity drawing wires 11, 11, and connection wires 12 . . . in such a solar cell module also reduce light transmitting through the rear surface, degrading an effect of the transmissive rear surface.